There are probably limits on how much companies can increase premiums for the unvaccinated. Under the Health Insurance Portability and Accountability Act—better known as HIPAA—employers generally are not allowed to charge workers extra for insurance based on their health status (the rule is somewhat similar to the Affordable Care Act’s regulations for the individual market). But federal law makes an exception for employer wellness programs, which can offer workers financial rewards or penalties to take steps such as quitting smoking. Vaccine surcharges would probably have to be structured under the same rules, which means the punishments for going without a shot can’t be so stiff that they can be considered “coercive”—a slightly fuzzy standard—and are limited to no more than 30 percent of the cost of individual coverage under the company’s plan. Delta seems to be keeping all of this in mind, though all their spokesman would tell me when I asked about it was that the company “is well within the plan and legal parameters to make this change.”

Simply mandating vaccines for employees might be the more straightforward and superior strategy as far as public health is concerned, compared to using the wellness program model. After all, there’s no question that businesses can outright require workers to get vaccinated before they return to the workplace (which, ironically, is a vastly more “coercive” option than any premium increase). And some hardline anti-vaxxers might choose to simply go without the shot or coverage, which could further isolate them from mainstream medical advice.